To begin, we have not been given the deed of agreement between the ACT government and Riverview (the Corkhill family), under which the government has signed over 40 per cent of profits, which will amount to hundreds of millions of dollars. As a result, the public knows very little of the financial arrangements behind this joint venture.

What we have been told is that the government and Riverview pay costs in a 60:40 split and share profits in a 60:40 split. The Corkhill family brings 332 hectares of land on the NSW side of the border to the deal, and the ACT provides 1000 hectares on the ACT side. The land isn't obviously 60:40, but Riverview says that the 60:40 split is based on the developable area, minus land set aside for conservation, schools, electricity lines and the landfill.

They say there will be 3260 homes on the NSW side and 5140 on the ACT side. But they claim the NSW contribution is worth more than that because it allows development right up to the ACT border rather than leaving a buffer. Without the border development, the ACT would only have space for 3080 homes, according to the proponents.

"Based on the land contribution and the projected financial outcome, a ratio of 60:40 was agreed as representative of each party's share of the project," the joint venture's website says. "This split was as a result of a rigorous assessment of the proposal by central government agencies all of which led to the ACT government endorsement of the project in May 2016."

It is time that contribution, that outcome and that rigorous assessment by all arms of government is laid on the table.

Without that, the farmers who have sold up their land along the city's western fringe will be justified in wondering whether they would have been better off hanging on to their land and demanding a joint venture for its development - and perhaps, like Riverview, they could also have arranged payment to manage those joint ventures. For that matter, any farmer still in possession of likely land would do well to put a "not for sale" sign at the gate pronto. With Riverview leading the way as development partners, selling is looking like a mug's game.

There is also a lack of clarity about what happens if the planning falls through on the NSW side of the border. That outcome is looking less likely after the Yass council's endorsement a fortnight ago - albeit with just four of the councillors voting yes, one no, and four absentees. The project now needs the NSW government's approval, and it is to be hoped that NSW applies more scrutiny and demands more transparency than either the ACT government and Yass have given to date.

Riverview says if NSW doesn't change its zoning to allow housing, its 332 hectares is forfeit to the ACT government. But it is incumbent on the government to disclose the numbers. How much is that land worth if it can't be developed? And what, in that arrangement, justifies the Corkhill family continuing to get 40 per cent of profits on the ACT side of the border?

The joint venture's less-than-satisfying answer is that if the NSW government does not approve development on its side of the border, the ACT housing estate would revert to just 508 hectares. The ACT government would get 60 per cent of that, which equates to 305 hectares and is still more than the "original base case scenario" of 300 hectares.

But that "extreme scenario", to use the joint venture's own words, would surely still leave Canberrans scratching their heads and wondering on what possible basis 40 per cent of the profits of a 508 hectare housing development had gone to a private family.

The questions here are around whether the ACT has done the best deal by the taxpayer and these are questions that can only be answered if we have access to the numbers. But based on the government's performance of late in managing land deals - to wit the strong of disorganised and ill-justified buy-ups of farm land along the western fringe - there is no obvious reason for comfort.